82 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



100 



90 



H 80 

 in 



70 



60 



50 



LU 



a. 



z 



LU 



cn 



LU 



0- 20 



10 



1/2 



1 V/2 



TIME IN YEARS 



21/2 



Fig. 12 — • Accelerated life tests on paper capacitors with various impregnants 

 at room temperature (60° to 80°F). 



herently stable and nonreactive. In addition, raw materials were care- 

 fully protected from contamination from the time of their manufacture 

 until they were used, or, wherever possible, they were cleaned and tested 

 for freedom from contaminants just prior to use. Unusually detailed 

 specifications were prepared for all materials. 



The effort to achieve extreme reliability also influenced or dictated a 

 number of design factors such as the minimimi wire diameters used in 

 wound apparatus, the use of as few electrical joints as possible and the 

 use of relati\'ely simple structures. These limitations resulted in the use 

 of unencased components in most instances. Wherever possible, the ends 

 of windings were used as terminal leads to avoid imnecessary soldered 

 connections. This injected the additional hazard of lead breakage owing 

 to handling during manufacture and inspection. This hazard was mini- 

 mized in most instances by providing the windings with extra turns 

 which were removed just before the component was assembled in the 

 network. Thus, the lead wires in the final assembly had never been sub- 

 jected to severe stress. Where this technique was impracticable, special 

 fixtures and handling procedures were used to prevent imdue flexing or 

 stressing of lead wires. 



As mentioned above there was one type of passive component in which 

 life is a function of time and severity of operating conditions. These are 

 the capacitors, especially those subject to high voltages. Because of this 



